Drive train and suspension for an autonomous ground vehicle

ABSTRACT

A skid-steer delivery autonomous ground vehicle has a drive train and suspension that aids in maneuverability. The AGV has six wheels, each of which is powered by its own motor. The AGV has features that diminish the dragging effect on the wheels, either by choice of wheel features or by taking weight off the front wheels during turning.

BACKGROUND

The present invention relates to autonomous vehicles, and moreparticularly to features of a drive train and suspension system fordelivery autonomous ground vehicles.

Autonomous ground vehicles are part of the growth of automated devices.One type of autonomous ground vehicle drives over sidewalks and likesurfaces for various purposes, including package delivery. In general,delivery AGVs have a control system that regulates voltage of the AGV'smotors to control its speed. A six wheeled delivery autonomous groundvehicle is known. Often, AGV are skid-steer type. United States PatentPublication Number 20180244327A1 discloses a six-wheeled vehicle with a“tilting lever” between two wheels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a delivery AGV of the type that canemploy the braking systems disclosed herein;

FIG. 2 is a top view with portions of the AGV removed to illustrate thedrive system;

FIG. 3 is another perspective view of the delivery AGV of FIG. 1 with aportion of the shell removed;

FIG. 4 is a bottom view of the delivery AGV;

FIG. 5 is an end view of a wheel assembly isolated from other parts,illustrating aspects of a means for reducing dragging;

FIG. 6 is a side view of the delivery AGV illustrating another aspect ofa means for reducing dragging;

FIG. 7 is another side view of the delivery AGV illustrating anotheraspect of a means for reducing dragging;

FIG. 8 is another side view of the delivery AGV illustrating anotheraspect of a means for reducing dragging; and

FIG. 9 is another side view of the delivery AGV illustrating anotheraspect of a means for reducing dragging.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

An autonomous ground vehicle (AGV) is a category of robot that mightoperate at times in an unprotected, uncontrolled environment. Becausethe AGV in some embodiments is intended to deliver packages to aresidence and/or business, the delivery AGV must be maneuverable intight spaces.

In general, an AGV of the type disclosed herein is a ground vehicle(typically unmanned) that operates, at least in some circumstances,without the need for a human controller, and at least at sometimes mayoperate in unprotected and uncontrolled environment. The AGV may usesensors to develop an understanding of the environment (sometimes only alimited understanding), which is then used by control algorithms todetermine the next action to take in the context of a human-providedmission goal.

An AGV, both in general and in the context of a delivery AGV disclosedherein, in an uncontrolled, unprotected environment may have the abilityto:

access information about the environment (such as maps of streets,sidewalks, and buildings, and in some cases building interiors);

detect people, obstacles (such as curbs, steps, bumps, slopes, and thelike), objects (such as landscaping, gates, and the like), and surfaces(such as lawns, cobblestones, sidewalk cracks and discontinuities, andthe like), and then evaluate and take action based on the detection; and

travel under its own power to waypoints, usually by battery power andwithout human navigation assistance, taking into account the aboveinformation and detection.

In some circumstances, an AGV's onboard control system may be able toautonomously learn, such as adjusting strategies based on input aboutthe surroundings, adapt to surroundings without outside assistance, andthe like.

A particular subset of autonomous ground vehicles is an AGV thatnavigates to a desired residential or commercial location to carry anobject, such as a package containing a commercial product. For example,United States Patent Publication Number 20180024554, titled “AutonomousGround Vehicles Based At Delivery Locations,” which is assigned to theassignee of the present invention, discloses AGVs that retrieve itemsfrom transportation vehicles (e.g., delivery trucks) for delivery tospecified locations (e.g., user residences, a commercial business,etc.). In various implementations, the AGVs may be owned by individualusers and/or may service a group of users in a given area (e.g., in anapartment building, neighborhood, etc.). The AGVs may travel out (e.g.,from a user's residence, apartment building, etc.) to meet atransportation vehicle (e.g., a delivery truck on the street) to receiveitems, and may be joined by other AGVs that have traveled out to meetthe transportation vehicle, and may line up in a particular order (e.g.,according to delivery addresses, etc.). After the items are received,the AGVs may travel back (e.g., to the user residences) to deliver theitems, and may be equipped to open and close access barriers (e.g.,front doors, garage doors, etc.). The AGV may also be equipped with alocked lid that can be opened only by an intended recipient.

The present invention uses the phrase “delivery AGV” or “AGV for packagedelivery” or other combinations of the terms “AGV” and “delivery” torefer to AGVs having the structure, capabilities and function tonavigate to a desired location, such as by navigating public or privatesidewalks or neighborhoods, to transport a package to a desired customeror residential or commercial location. Accordingly, a delivery AGWincludes an internal chamber for holding a package payload and islimited in speed, such as to 6 mph, 10 mph, or 15 mph, as determined bythe particular design guidelines and possibly by state regulation. Inthis regard, these speeds are referred to herein as low speed.

The AGV disclosed herein is driven by six motorized drive wheels. Noneof the wheels are steered in that each wheel is fixed in astraight-ahead direction. Changing direction is achieved by moderatingthe wheel speed, according to well-known algorithms. In the embodimentof the figures, the rear wheels are supported by the body of the AGV.The mid-wheels and the front wheels are connected together by a bogiearm connected to the AGV body by a bogie shaft. Other configurations,such as the bogie arm connecting the mid wheels and rear wheels, arepossible. The bogie shaft can pivot, and thus the bogie arm can pivot ina see-saw action about the bogie shaft.

The AGV has a skid steer system, in which the direction of the drivewheels are fixed in a straight line, as illustrated in FIG. 2. In theexample illustrated in FIG. 2, each one of the left wheels is powered byits motor in a forward direction while each one of the right wheels ispowered by its motor in a rearward direction. In some circumstances,depending on the location and speed of the wheels, the AGV will pivotabout a pivot equidistant between the front and rear wheels. Each one ofthe front and rear wheels will have a lateral velocity component (thatis perpendicular to its front-rear or longitudinal direction) during theprocess of changing direction such that the wheels skid over thesurface. Moreover, in circumstances in which the center or turning isnot constant or not aligned relative to the center wheels, the centerwheels can also undergo dragging. FIG. 2 illustrates the longitudinaldirection L1 and the lateral direction L2. FIG. 5 illustrates wheeldeflection, illustrated by a dashed curve line D to represent thedeformation of the centerline of a corner tire during dragging.

Dragging of the wheels laterally requires large motor torque from thewheel motors and can cause vibration or chattering that can betransmitted to the body of the AGV, which can be detrimental toelectronics. The dragging phenomenon having the drawbacks of large motortorque and/or vibration is referred to herein as dragging. The draggingproblem is exacerbated for a delivery AGV that is lightweight tooptimize power requirements and that six powered wheels, each of whichis non-steered.

The means for diminishing dragging include tire design and diminishedthe load on the corner wheels, as explained more fully below.

As best illustrated in FIGS. 1-4, a delivery AGV 10 disclosed hereinincludes an upper body 12, a lower body 112, a wheel and suspensionassembly 18, a power supply system, and a control system. Upper body 12includes a shell 301, a cargo bay 30, front and rear sensors behindcorresponding front and rear windows 341 and 351 in the shell, and a lidassembly 26.

Lower body 112 includes a chassis 110 and a skin or shell assembly 201.Chassis 110 in the embodiment of the figures is formed of sheet aluminumplates, including a bottom wall 120, left and right sidewall 130L and130R, a front wall 140, and a rear wall 150 (bottom wall, right sidewall, front wall and rear wall are not shown). The walls are affixedtogether, such as by rivets or other conventional means, to form astructure that is unitary and capable of supporting AGV 10. Chassis 110has an open top and forms a hardware bay for a power system, asdescribed below. A processor for overall control and communicationfunctions can be within chassis 110 or proximate front or rear sensorsthat are located behind front and rear windows 341 and 351,respectively.

A rear portion of bottom wall 120 and a bottom portion or rear wall 150merge into a transverse structure 160, which forms a lowermost portionof chassis 110 and provides structural support for the rear wheelassemblies. Transverse frame 160 includes structure features formingrear wheel assembly interfaces. A forward portion of chassis 110includes holes or cutouts forming front wheel assembly interfaces 190,which in the figures is a plate added to side wall 130. For example, aplate of a hub motor can be bolted to the chassis and interfaces 190.Other configurations are contemplated.

The walls of the chassis include structural and functional features thatdepend on the particular application, including a tapered nose (that is,front walls 140 tapers when viewed in top view), various openings, tabs,structural cross-members, and the like. The walls of chassis 110 can beformed of any material suitable for supporting the panels and wheelassemblies as the AGV carries the intended load. Aluminum sheet metal isused in the embodiment of the figures. The thickness, specific material,use of stiffeners and other structural supports, and other decisionsrelating to the material choice and properties can be made according tothe particular goals of the AGV, including strength, weight, and likeparameters.

Shell 201 is formed of overlapping polymer panels held to chassis 100 byfasteners, such as screws. Shell 301 is formed by overlapping polymerpanels held to structural columns. The panels of shell 301 overlap thepanels of shell 201.

Upper body 12 includes a lockable, hinged lid 26 that covers and securespackages held in a cargo bay (not shown in the figures). Lid 26preferably is locked in a manner that enables unlocking by the intendedrecipient by any means locking and opening means.

As illustrated in FIG. 2, the power system includes batteries (notshown), motor controllers 610, voltage regulators 620, power board 630,and other components, as needed, to supply and regulate power to thedrive wheel assemblies.

Wheel and suspension assembly 18 includes three pairs of drive wheelsassemblies: rear drive wheel assemblies 750R, mid drive wheel assemblies750M, and front drive wheel assemblies 750F. As illustrated in thefigures, rear drive wheel assemblies 750R are supported by transverseframe 160 of the chassis at wheel interface 190. Mid and front wheelassemblies 750M and 750F and connected via a bogie system 760. The bogiemechanism 760 includes an axle or shaft 762 and a bogie arm 764 coupledto an outboard end of shaft 762. Shaft 762 extends through skin 201 andis supported at the front wheel interface 190 of chassis 110. Bogie arm764 pivots relative to a centerline of shaft 762. The structuredisclosed herein is not limited to a fixed shaft 762 on which arm 764pivots, or a pivoting shaft 762 to which arm 764 is rigidly attached orpivotable, or other configuration unless specified in the claim.

Consistent with the convention throughout the description, referencenumber 750 is used to refer to structure common to all wheel assemblies.Each one of drive wheel assemblies 750 includes a hub-type drive motor752, which preferably is conventional, and a wheel 754 powered by drivemotor 752.

Each wheel 754 includes a tire 756 and a disc 720 that is affixed to therotor or output shaft of the drive motor 752 and the tire 756. Tire 756preferably is formed of a solid rubber, a polymer, or like material. Acommon process is injection molding or over-molding the tire material ona polymer disc, such as disk 720.

AGV 10 includes a means for diminishing dragging. The means fordiminishing dragging may include tread of tire 756 chosen to diminishdragging. The tread pattern can affect friction and the propensity fordragging. A tread 759, an example of which is illustrated in FIG. 5,includes grooves or channels. To diminish dragging, generally, a tiretread can include various components. For the example shown in FIG. 5, atire tread that only has grooves parallel to the axis of rotation of thetire may be employed. Further, grooves that are neither parallel to theaxis of tire rotation nor parallel with the direction of straight-aheadmovement L1 of the tire (which is perpendicular to the tire rotationaxis L2) are referred to herein as “oblique.” Oblique tread componentsare illustrated schematically by an angle A of FIG. 5. Treads having anoblique component are contemplated.

The force applied by the ground to the tire at the groove when the AGVis undergoing turning in a skid steer configuration (that is, the forcein direction L2 that in skid steer systems causes dragging), can include(depending on the circumstances) a force component in the straight-aheaddirection L1 such that the force rotates the tire, thereby diminishingdragging. In this regard, as the tire encounters dragging conditions,some of the force applied in the direction L2 is transmitted to by thesurface of the tread 759 (such as but not limited to oblique treadcomponents) into a force that tends to rotate tire 756, which relievesthe energy build up that can cause dragging. Tire 756 can have a thinnedportion 802 radially inboard to the contact portion 804 of tread 759 todiminish dragging. This configuration is referred to herein asmushroom-shaped, which shape is believed to diminish the magnitude ofdragging.

The means for diminishing dragging can also include a tire material thatdiminishes vibration when undergoing dragging. The tires 756 of the AGVcan be solid tires, which often have a durometer of at least shore 65A.Preferably, the tires 756 are formed of a material having a durometer ofno more than 60A, or no more than shore 50A, and more preferably no morethan shore 40A. Further, layers of different materials having differentdurometers to diminish vibration likelihood, vibration amplitude, and/orvibration frequency may be employed. The exact stiffness chosen for thetire material depends on the geometry of the tire, as the valuesprovided herein are for example or illustration.

The tire features for diminishing dragging may be applied to any of thetires 756 of rear, mid, and front wheels 750R, 750M, and 750R. Thecorner wheels 750R and 750F are expected to encounter greater draggingthan mid wheels 750M, and thus is possible that the tire featuresdescribed herein are applied only to front wheels 750F, only to cornerwheels 750R and 750F, only rear wheels 750R, or all wheels 750R, 750M,and 750F.

The means for diminishing dragging can also include diminishing the loadon the corner wheels that are in position to experience dragging. Insome embodiments, the load on a first one of the corner drive wheels(that is, either the front drive wheel 750F or rear drive wheel 750Rthat is attached to bogie arm 764 opposite to mid drive wheel 750M) isdiminished by transferring load from the first drive wheel to mid drivewheel 750M. The effect of increased load on mid drive wheel 750M in mostcircumstances reduces the load on all corner wheels 750R and 750F.Accordingly, the structures and functions in this regard are referred toa means for diminishing the load on the corner wheels.

According to a first embodiment drag diminishing system 810 illustratedin FIG. 6, a motor control reduces the load on the front wheels 750F,while AV is at rest, rotating the mid drive wheel 750M by an angle deltawhile the rear wheels 750R are fixed. In the side view of FIG. 6, theclockwise rotation of mid wheel 750M puts load on mid wheel 750M and onrear wheel 750R while reducing load on front wheel 750F.

Drag diminishing system 810 may also function while AGV is in motion.For example, when AGV 10 is moving forward, the controls can increasemid drive wheel 750M speed relative to front wheels 750F. Theacceleration of mid drive wheels 750M during this process reduces theload on front wheels 750F, as illustrated by the arrow indicating amoment applied about bogie shaft 762 in FIG. 6.

System 810 may include one or more sensors to indicate the functioningof the drag diminishing system. An encoder 812 may be located at shaft754 to indicate the position of bogie arm 764. Other sensors (not shown)may be employed, such as load cells to indicate load on each wheelassembly, accelerometers, and the like.

System 810 relies on the differential in rotational position of themiddle and rear wheels relative to the front wheels, the load of frontwheel 750F on the ground is diminished. In some circumstances, themiddle wheel rotational position is slightly ahead of the nominalposition of the nominal rear wheel position in order to diminish thefront wheel load. System 810 can work with a mechanical lock, asexplained below.

System 830 for diminishing dragging reduces load on front wheel 750F bymechanical means. For example, a spring 832 or other means (not shown)can provide an upward force on wheel 750F or a portion of bogie arm 764forward of shaft 754. Alternatively, spring 832 of other means could puta downward force on bogie arm 764 rearward of shaft 754. Spring 832 canbe placed at any position such that the spring imparts and upward forceon wheel 750F. For merely one example, a bracket 834 can extendlaterally from chassis 110 beneath the front portion of bogie arm 764such that spring 832 is between bracket 834 and the underside of bogiearm 764. Spring 832 in compression then applies an upward force on theforward portion of bogie arm 764.

Spring 832 can include a release such that the upward force is appliedonly when turning, and can be disengaged when moving forward and/or whencurb climbing or stair climbing. In this regard, bracket 834 can betranslated up and down to engage and disengage, respectively, spring832. Or bracket 834 could be pivoted down to release the force appliedto the forward portion of arm 756 (that is, disengage the spring) andthen be pivoted upwardly into position to enable spring 832 to apply theupward force (that is, engage the spring).

Other mechanical means are contemplated. For example, a releasabletorsion spring can be applied to the shaft 765 of mid drive wheel 750Mand/or front drive wheel 750F to apply the downward force on front wheel750 when desired. The orientation of the torsion spring on front wheel750F is opposite the orientation of the torsion spring on mid wheel750M. Further, an actuator may replace the spring. For example, anelectric linear actuator may be used in place of or in addition tospring 832. For example a screw type actuator, a solenoid, and the likecan be used to create the upward force described above. Pneumatic,hydraulic, other conventional linear actuators may be employed.

A third means 850 for diminishing front wheel dragging includes a motor852 mounted such that it drives bogie arm 764 to apply a torque on bogiearm 764, and thus increase load on mid wheel 750M (counterclockwise inFIG. 8) and reduce the load on front wheel 750F. Motor 852 can be anytype, such as a servomotor or stepper motor, or other. Motor 852 iscontrolled by the control system such that it may be disengaged (thatis, turned off) during normal operation and engaged to diminish to loadon front wheel 750F when desired. An encoder on the motor 852 or bogiearm 764 may be employed.

AGV 10 can include a lock 850 that holds bogie arm 764 in position uponfront wheel 750F having a diminished load. The lock can be a mechanicallock or clamp can be of any type, as any of the many commercial clampsbased on friction, detents, and the like may be employed. Lock 870 isillustrated schematically in FIG. 9 to indicate its use. Lock 870 may beemployed anywhere convenient, and may be actuated by an electricactuator associate with the type of mechanical lock, and preferably is asolenoid or solenoid controlled.

Lock 870 may be employed with any of the means for diminishing draggingdisclosed herein, such as means 810, 830, and/or 850. For example, theload on front wheel 750F may be diminished by means 810, 830, and/or850, and lock 870 may be employed to hold bogie arm 764 in the positionin which the load to front wheel 750F is diminished.

In practice, any and all of the tire design features and means fordiminishing dragging may be employed in any combination. As an exampleof the operation of AGV 10, upon a determination from the control systemor from a remote control that AGV 10 should turn or pivot, drive thewheels on one side of the AGV can rotate one direction (forward orrearward) while the wheels on the other side of the AGV operation in theother direction (rearward or forward, respectively). The speed of thedrive wheels can be moderated to diminish dragging of rear wheels 750R,relying on the dragging reducing mechanisms disclosed herein to reducedragging of front wheel 750F.

Upon application of an upward force (that is, a diminished load) onfront wheels 750F, lock 870 may engage to hold front wheel 750F andbogie arm 764 in a position in which some of the load normally on frontwheel 750F is transferred to mid wheel 750M. The reduced load on frontwheel 750F and the dragging diminishing tire design are believed toimprove or eliminate vibration and undue drag forces at front wheel750F.

The control algorithms for controlling the straight-ahead movement,turning, and rotating AGV 10 are well known, as will be understood andemployed by persons familiar with battery powered vehicles.

Control system 50 includes sensors 52F and 52R and other components andsystems used for navigation and guidance, avoiding objects,image-capture and sensing, power management, communications, security,and other functions inherent in achieving the goals of a delivery AGV.Sensors 52F and 52R can be mounted behind a forward facing panel 341and/or a rearward facing panel 351. Sensors 60 can include camerashaving images sensors including image signal processing, light sensors,and the like, with corresponding processing including image decoding,lens correction, geometrical transformation, video stream transcoding,video analytics, image capture, and compression to provide obstacledetection and obstacle identification. Sensors for determining speed mayalso be employed. Panel 28F (and 28R) can be transparent polymer, suchas (for example) acrylic, Plexiglas, or polycarbonate.

Sensors 52F and 52R can include RADAR sensors, such as SRR (Short-rangeradar) applications and MRR/LRR (mid-range radar, long-range radar)applications; LIDAR sensors, such as infrared LIDAR systems that withthe aid of a Micro-Electro-Mechanical System (MEMS), which use arotating laser, or a solid-state LIDAR. Control system 50 can alsoinclude GPS modules, inertial guidance modules such as an inertialmeasurement unit (IMU) having gyroscopes and accelerometers (preferablyin each of the x, y, and z directions), power management modules tocontrol power, overall consumption, and thermal dissipation. Othermodules, components and functions are contemplated.

Control system 50 and sensors 52F and 52R may also be employed incontrolling the driving and turning of AGV 10 during normal conditions.For example, a speed sensor on the wheels, sensors on motor currentand/or voltage, GPS, accelerometer, gyroscope, optical sensors, and thelike may be employed to determine a safe straight-ahead speed, safeturning radius and velocity for the vehicle and package (taking intoaccount the possibility of encountering a person who might not see or beexpecting the vehicle), safe stopping distance to provide feedback tothe controller for determining the speed, and the like.

Control system 50 may also include a package delivery module andcorresponding sensors. For example, a sensor can be associated with aclosed position of lid 26 to assure that a package to be delivered to aresidential or commercial destination is secure in chamber 24 duringtransport. A means for unlocking a lock on lid 26 (or unlocking anactuator for lid 26 or like means) can include a keypad, a wirelesscommunication system (for working with Wi-Fi, cellular data, Bluetooth,NFC or other communication means to send a signal to the lock uponverification), a facial or fingerprint recognition module, or the likemay also be included.

Control system 50 controls the movement of AGV 10 to a desireddestination, the delivery of a package within chamber 24 to anauthorized recipient, and/or movement of AGV 10 to a home location. Inthis regard, the description of control system 50 and sensors 52F and52R, and United States Patent Publication Number 20180024554 and/orindustry practice in view of the present disclosure may inform thefunctions in this regard.

It is, of course, the goal of control system 50 to avoid unintentionalcontact, especially for people, pets, and the like. Contact is referredto herein as transient contact to distinguish it from intentional,low-force contact (such as opening the lid to access a package) andcontact over a significant period, such as leaning against or placing afoot on the robot, of the type that is not a risk, or is a low risk, ofinjuring a person. In the event of transient contact, the energyabsorbing means disclosed herein are intended to diminish the magnitudeof energy transmitted to a person by an AGV, compared with an unmodifiedsolid or rigid surface of prior art AGVs currently commercialized.

The present invention has been illustrated by using examples of possibleembodiments. The present invention is not limited to the structure,function, and/or materials set out herein. Rather, it is intended thatthe invention be given its broadest appropriate scope.

We claim:
 1. A skid-steer delivery autonomous ground vehicle (AGV)having a drive and suspension system, the delivery AGV comprising: twopairs of opposing independent corner drive wheels coupled to a chassisof the AGV; a pair of opposing mid drive wheels; a bogie suspension oneach side of the body connected to the chassis and connected between themid drive wheels and a first one of the pairs of drive wheels; and meansfor diminishing dragging of at least one of the corner drive wheelsduring turning, the means for diminishing dragging including at leastone of tire configuration features and a means for diminishing a load onthe corner drive wheels while the AGV is at rest.
 2. The AGV of claim 1wherein the bogie suspension includes a pivotable bogie shaft connectedto a chassis of the body of the AGV and a bogie arm at a distal end ofthe bogie shaft, the mid drive wheel coupled to a first end of the bogiearm, the first one of the corner wheels coupled to an opposing end ofthe bogie arm, the first one of the corner wheels being one of the frontdrive wheel and the rear drive wheel.
 3. The AGV of claim 2 wherein themeans for diminishing dragging is a tire with a tread that reducesdragging, wherein the tread includes components parallel to an axis ofrotation.
 4. The AGV of claim 3 wherein the tire has a durometer chosento diminish dragging and based on a tire geometry.
 5. The AGV of claim 3wherein the means for diminishing dragging is the tire having a mushroomshaped cross section.
 6. The AGV of claim 3 wherein the means fordiminishing dragging includes a means for diminishing the load on thecorner drive wheels relative to a load on the mid drive wheels while theAGV is at rest.
 7. The AGV of claim 6 wherein the means for diminishingthe load on the corner drive wheels includes a control system adaptedfor rotating the mid drive wheel relative to the first drive wheel suchthat the load on the first drive wheel is reduced.
 8. The AGV of claim 6wherein the means for diminishing the load on the corner drive wheelsincludes a biasing mechanism for applying a force to the bogie arm in anorientation to produce an upward on the first drive wheel.
 9. The AGV ofclaim 7 wherein the biasing mechanism is releasable, whereby the biasingmechanism is adapted for releasing the force applied to the first drivewheel.
 10. The AGV of claim 6 wherein the means for diminishing load onthe corner drive wheels includes a motor adapted for providing a torqueto the bogie arm in an orientation that applies an upward force to thefirst drive wheel.
 11. The AGV of claim 6 wherein the means fordiminishing load on the corner drive wheels includes a means forapplying an upward force to the first drive wheel and a lock adapted forholding the first drive wheel in a diminished load state.
 12. The AGV ofclaim 2 wherein the bogie suspension is connected between the mid drivewheel and the front drive wheel, and the bogie arm is coupled to the middrive wheel and the front drive wheel.
 13. A delivery autonomous groundvehicle (AGV) having a drive and suspension system, the delivery AGVcomprising: a body for carrying a package; six motorized, skid steerdrive wheels; the six drive wheels including, on opposing sides of thebody: two pairs of corner drive wheels and a pair of mid drive wheelsbetween the corner drive wheels; a bogie suspension on each side of thebody connected between the mid-wheel and at least a first one of thecorner wheels; and means for diminishing dragging of at least one of thecorner drive wheels.
 14. A method of operating a delivery autonomousguided vehicle comprising: in a delivery AGV of claim 13, providingpower to the drive wheels such that the AGV undergoes a tight turn; anddiminishing dragging on the corner drive wheels by engaging a means fordiminishing a load on the corner drive wheels.
 15. The method of claim14 further including the step of diminishing dragging by rotating a tirevia tire configuration features during the tight turn.
 16. The method ofclaim 14 further including the step of engaging a lock to hold the meansfor diminishing the load in an engaged position.
 17. The method of claim16 wherein step of diminishing the load on the corner drive wheelsincludes rotating the mid drive wheel relative to the first drive wheelsuch that the load on the first drive wheel is reduced.
 18. The methodof claim 16 wherein step of diminishing the load on the corner drivewheels includes applying a biasing force to a bogie arm in anorientation to produce an upward force to the first drive wheel.
 19. Themethod of claim 16 wherein step of diminishing the load on the cornerdrive wheels includes providing a torque to the bogie arm in anorientation that applies an upward force to the first drive wheel.